RE: [PATCH 3/5] ACPI / sleep: EC-based wakeup from suspend-to-idle on Dell systems

[Zheng, Lv]

Hi,

> -----Original Message-----
> From: linux-acpi-owner@xxxxxxxxxxxxxxx [mailto:linux-acpi-owner@xxxxxxxxxxxxxxx] On Behalf Of Rafael J.
> Wysocki
> Sent: Friday, April 28, 2017 6:26 AM
> To: Mario.Limonciello@xxxxxxxx
> Cc: linux-pm@xxxxxxxxxxxxxxx; andriy.shevchenko@xxxxxxxxxxxxxxx; dvhart@xxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; linux-acpi@xxxxxxxxxxxxxxx; srinivas.pandruvada@xxxxxxxxxxxxxxx;
> tglx@xxxxxxxxxxxxx; mika.westerberg@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH 3/5] ACPI / sleep: EC-based wakeup from suspend-to-idle on Dell systems
> 
> On Thursday, April 27, 2017 02:47:59 PM Mario.Limonciello@xxxxxxxx wrote:
> > > -----Original Message-----
> > > From: Rafael J. Wysocki [mailto:rjw@xxxxxxxxxxxxx]
> > > Sent: Wednesday, April 26, 2017 4:24 PM
> > > To: Linux PM <linux-pm@xxxxxxxxxxxxxxx>
> > > Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>; Darren Hart
> > > <dvhart@xxxxxxxxxxxxx>; LKML <linux-kernel@xxxxxxxxxxxxxxx>; Linux ACPI <linux-
> > > acpi@xxxxxxxxxxxxxxx>; Srinivas Pandruvada
> > > <srinivas.pandruvada@xxxxxxxxxxxxxxx>; Thomas Gleixner <tglx@xxxxxxxxxxxxx>;
> > > Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>; Limonciello, Mario
> > > <Mario_Limonciello@xxxxxxxx>
> > > Subject: [PATCH 3/5] ACPI / sleep: EC-based wakeup from suspend-to-idle on Dell
> > > systems
> > >
> > > From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > >
> > > Some recent Dell laptops, including the XPS13 model numbers 9360 and
> > > 9365, cannot be woken up from suspend-to-idle by pressing the power
> > > button which is unexpected and makes that feature hardly usable on
> > > those systems.  However, on the 9365 ACPI S3 (suspend-to-RAM) is not
> > > expected to be used at all (these systems ship with Windows 10 using
> > > Modern Standby which never exercises the ACPI S3 path) and
> > > suspend-to-idle is the only viable system suspend mechanism in there.
> > >
> > > The reason why the power button wakeup from suspend-to-idle doesn't
> > > work on those systems is because their power button events are
> > > signaled by the EC (Embedded Controller), whose GPE (General Purpose
> > > Event) line is disabled during suspend-to-idle transitions in Linux.
> > > That is done on purpose, because in general the EC tends to generate
> > > tons of events for various reasons (battery and thermal updates and
> > > similar, for example) and all of them would kick the CPUs out of deep
> > > idle states while in suspend-to-idle, which would not be desirable.
> > >
> > > Of course, on the Dell systems in question the EC GPE must be enabled
> > > during suspend-to-idle transitions for the button press events to
> > > be signaled while suspended at all.  Fortunately, there is a way to
> > > tell the EC to stop generating the non-wakeup events, which is by
> > > using the _DSM object under the so called micro-PEP (uPEP) device
> > > provided to support Modern Standby in Windows 10.
> > >
> > > The expected way to use it is to invoke function 0 from it on system
> > > initialization, functions 3 and 5 during suspend transitions and
> > > functions 4 and 6 during resume transitions (to reverse the actions
> > > carried out by the former).  In particular, function 5 from the uPEP
> > > device _DSM causes the EC to become less verbose (so to speak) on the
> > > affected systems and then its GPE can be enabled as a wakeup source
> > > (then, on resume, function 6 switches it back to the "working state"
> > > mode).
> > >
> > > In support of the affected Dell systems, implement the uPEP device
> > > handling as described and allow the EC to generate system wakeup
> > > events if that device is present and behaves as expected.  Enable
> > > that for Dell only, as there are other systems out there in which
> > > the uPEP device is exposed in the ACPI tables and its _DSM appears
> > > to be functional, but it actually isn't, whereas Dell is committed
> > > to supporting it.
> > >
> >
> > I am of course biased in that my priority is for this to work for Dell.
> > Dell is definitely committed to supporting this on any system with
> > the low power idle bit in the FADT set.
> >
> > So I'm fine with the current proposed solution, but have you
> > dug into what actually breaks on this other system?  Does it actually
> > work with Modern Standby + the uPEP device on Windows 10?
> >
> > To my understanding I would think any OEM that is enabling this
> > uPEP device it should be getting called by the Windows kernel
> > identically when entering resiliency phases.
> >
> > This makes me wonder if it should be inverted and a blacklist
> > of platforms that the uPEP device doesn't work.
> 
> For now I'd prefer to only do it on platforms where the benefit is clear.
> 
> The next step may be to extend it to the other ones, but let's avoid making
> what is problem mitigation really depend on things that may or may not
> work elsewhere to start with.

Then is it possible to invoke acpi_mark_gpe_for_wake() (and maybe also acpi_unmark_gpe_for_wake()) right after invoking uPEP functions?
So that such platform specific stuffs won't go into ec.c.

Thanks and best regards
Lv